Various techniques are known for digital printers to provide continuous tone (monochrome or color) printing. Traditional offset printing systems compensate for tone nonlinearity through the measurement of dot gain. Dot gain is the percentage of spot size increase of a 50% intensity dot. This dot gain is corrected in the production of the printing plates. Further correction can be done through adjustment of the pressure between the transfer media and the printing plate. The object is to obtain a linear tone scale from the lightest to the darkest shade of a given ink in the printing system.
High speed digital ink jet printing systems apply the ink directly to the substrate as directed by the input data. In certain digital printing systems the application of a linear gradation of ink to a substrate does not result in the appearance of a linear gradation in tone. The image data must be corrected so that tone linearity can be achieved on a particular substrate. In the past, it has been necessary to print and measure the resulting tone from samples of a number of printed ink levels in order to determine the appropriate data transformation. This transformation was then applied to the image data.
Typically, printing system configurations and substrates differ in acceptable maximum ink limit. Problems in image quality, such as edged definition and loss of detail in the shadow areas, can result. Image quality and ink drying time varies significantly with the substrate As conditions of the printing system and substrate type change regularly, it is often necessary to determine new data transformations that redefine the tone curve shape and upper ink limit for each ink in the system.
It would be desirable to be able to determine an appropriate transformation for application to images to be printed on the given system and substrate.